Self-locking fastener

ABSTRACT

A self locking fastener ( 30 ) including a blind bore ( 12 ) sized to recieve a male threaded component, the male threaded component engaging or forming a complementary thread on at least part of inner surface of the blind bore ( 12 ), at least one first part of the bore ( 12 ) being an interference fit with the thread of the male threaded component.

TECHNICAL FIELD

This invention relates to fasteners and more particularly toself-locking fasteners or nuts that connect to an exposed threaded boltor axle and protect the end of the bolt or axle from damage.

BACKGROUND ART

In many applications self-locking fasteners are required. Self-lockingfasteners exist, but these comprise a conventional nut with a hollowNylon insert on the outer end. Peening part of the nut over the insertretains the Nylon insert, but this is complex and expensive. In someapplications where a nut is placed on the end of a bolt, threaded axleor rod or similar object having a male thread formed thereon(hereinafter referred to as a bolt) to secure an item, the bolt extendsthrough the nut and is thus exposed to damage. If the thread becomesdamaged it may be impossible to replace the nut without recutting thethread on the bolt. Severe damage may result in the need to replace thebolt. Where the bolt is part of another component, severe damage to thebolt may require replacement of the entire component.

DISCLOSURE OF THE INVENTION

In one broad form the present invention provides a self lockingfastener, the fastener including of a resilient material, the resilientmaterial having an inner end and an outer end and including a blindcylindrical bore extending into the fastener from the inner end, thebore having an open end and a closed end, wherein at least a first partof the bore is adapted to receive a male threaded component, and whereinthe first part of the bore is unthreaded and has a diameter such thatthe male threaded component forms a female thread in the surface of thefirst part when screwed into the bore.

The bore may be of constant diameter or may be tapered. A tapered boreis preferred over a bore of constant cross section.

The fastener is preferably formed of a polyamide, such as Nylon and morepreferably of PA 6E Nylon. Other resilient plastics or other resilientmaterials may be used.

In preferred forms of the invention the bore includes a second partadjacent the open end that is of a larger diameter compared to the firstpart. In some forms of the invention the second part may be cylindricalbut of a slightly larger diameter, so as to aid centring of the fasteneron the male threaded component. The second part may have a constantdiameter or may be tapered. In other forms of the invention the secondpart may be a recess sized to receive a conventional nut.

The fastener, in some forms of the invention, has a cylindrical outersurface. In other forms the outer surface may have a hexagonal or otherpolygonal outline. The outer end of the fastener may be flat, partspherical or part elliptical or any other shape. In preferred forms ofthe invention the outer end is in the shape of a truncated cone.

Where the outer surface of the fastener has a circular outline,preferably the outer end includes structures by which the fastener maybe rotated. In preferred forms of the invention there are provided twoor more recesses or bores to aid rotation. Preferably the recesses areprovided as one or more pairs of diametrically opposed recesses.

Preferably the inner end of the fastener is substantially planar. Insome forms of the invention the inner end may include one or moreprotrusions extending axially from the generally planar end. Theprotrusions may be one or more annular rings or arcs coaxial with thebore. In preferred forms of the invention a single annular ring isprovided with an inner diameter substantially the same as that of theouter part of the bore.

The inner end of the fastener may also include retaining structures toretain or position a sealing and/or lubrication pad, gasket or seal onor adjacent the end of the fastener. In preferred forms theprotrusion(s) on the inner end also serve this function.

In some forms of the invention the outer periphery of the fastenerincludes one or more radially extending protrusions, more preferably atleast one radially extending ring.

In further forms of the invention, the fastener includes a bore having athreaded portion and an interfering portion that engages and interfereswith the thread of the bolt that is screwed into the threaded component.In one form the threaded portion is provided by one component and theinterfering portion is provided by a second component. In one form thesecond component is a washer that has a bore through which the threadedbolt passes. The bore of the washer is smaller than the maximum diameterof the threaded bolt and preferably smaller than the minimum diameter ofthe threaded bolt and so permanently interferes with the bolt, therebyresisting rotation of the fastener relative to the bolt, whether thefastener is tight or not.

In further forms of the invention of the interfering portion may be partof or may be mounted on or in a component that provides the threadedportion. The interfering portion extends into the volume through whichthe bolt passes, so as to engage the bolt as it is threaded on to thethreaded component. The interfering portion may be provided by one ormore separate components and these components may be one or more plugsor inserts of a resilient material located in the thread of the threadedportion. These plugs may be cylindrical or longitudinal inserts. Theplugs may be received within respective recesses in the wall of thethreaded portion. These recesses may also extend through the wall of thethreaded portion.

In other forms part or all of the threaded portion may be formed so thatthe thread has a diameter smaller than normal for the male thread, sothat when engaged the reduced diameter thread creates additionalresistance against rotation of the male thread in the female thread.

The threaded component is preferably encased in a shell that closes thebore into which the bolt enters, thereby protecting the free end of thebolt. The shell may have an internal bore into which the bolt extends.The threaded component preferably has an outer surface that prevents therotation about the axis of the threaded bore of the threaded componentrelative to the shell in which it is encased. In its broadest form, theouter surface of the threaded component merely requires a portion thatis non-circular when viewed axially.

The threaded component also preferably has an outer surface thatprevents the threaded component being pulled out of the shell axially,such as when the fastener is tightened. In its broadest form the outersurface of the threaded component has first and second portions encasedin the shell with the second portion is located axially inwardly in theshell relative to the first portion and which extends radially furtherfrom the axis than the first portion. In a preferred embodiment thethreaded component includes a planar hexagonal portion that serves toprevent rotation of the threaded component of relative to the shell. Ina preferred embodiment the threaded component also has a cylindricalportion and a hexagonal portion that is located at the inner end of thecylindrical portion. The hexagonal portion is encased in the shell andat least part of the cylindrical portion is also encased in the shell.The hexagonal portion extends radially more than the cylindrical portionand so prevents the threaded component being pulled out of the shell androtated relative to the shell.

In a preferred embodiment, the recesses provided in the shell to enablethe shell to be tightened onto the bolt extend to a washer provided asan interfering component that is encased in the shell. Duringmanufacture the threaded component and the interfering washer aremounted on to a pin that extends into a plastics injection-mouldingcavity. Another part of the cavity is provided with two second pins thatextend through the cavity and engage the washer and push it and thethreaded component tightly against each other. Plastics material is theninjected into the cavity so forming the shell and encasing the threadedcomponent and the interfering washer in the shell material. The firstpin is a relatively tight fit into the bore of the washer andaccordingly no shell material, or very little shell material, escapesfrom the cavity via any gaps between the washer and the first pin intothe thread area of the threaded component. The two retaining pins formthe recesses that in the finished product are used for tightening thefastener. The first pin extends beyond the washer and so forms a blindbore in which the free end of the bolt to which the fastener may beattached may extend into. By using a first pin of a constant diameterand a suitable material for the shell this blind bore may also serve tointerfere with the thread of the bolt and so restraint or preventrotation of the fastener relative to the bolt, irrespective of whetherthe fastener is tight or not.

It will be appreciated that the invention is not limited to manufactureby a plastics injection-moulding process and that other materials andprocesses may be used. Examples of other processes include die castingand pour casting. Other materials that may be used include metals,ceramics and other polymers such as if urethanes.

The invention will be better understood from the following, non-limitingdescription of preferred embodiments and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of a first embodiment of the invention;

FIG. 2 is a cross sectional view taken along line AA of FIG. 1;

FIG. 3 is a top view of a second embodiment of the invention;

FIG. 4 is a cross sectional view taken along line AA of FIG. 3;

FIG. 5 is a top view of a third embodiment of the invention;

FIG. 6 is a cross sectional view taken along line AA of FIG. 5;

FIG. 7 is a top view of a fourth embodiment of the invention, and

FIG. 8 is a cross sectional view taken along line AA of FIG. 7;

FIG. 9 is a perspective sectional view of a 4th embodiment of theinvention;

FIG. 10 is an exploded perspective view of the embodiment of figurenine;

FIG. 11 is a cross sectional view of the embodiment of FIG. 9 takenalong the axis;

FIG. 12 is a perspective view of a nut component of the embodiment offigure nine;

FIG. 13 is an axial cross sectional view of the nut of FIG. 12;

FIG. 14 is a perspective view of a washer component of the embodiment ofFIG. 9;

FIG. 15 is a side view of the washer of FIG. 14;

FIG. 16 is an end view of the washer of FIG. 14.

FIG. 17 is an end view of the fastener of FIG. 9;

FIG. 18 is an axial cross-sectional view of the shell of the fastener ofFIG. 9;

FIG. 19 is a reverse perspective view of the fastener of FIG. 9;

FIG. 20 is an axial cross sectional view of a first variation of the nutcomponent of FIG. 12.

FIG. 21 is an axial cross sectional view of a second variation of thenut component of FIG. 12.

FIG. 22 is a plan view of an alternative washer for use with theembodiment of FIGS. 9 to 19;

FIG. 23 is an axial cross sectional view of an alternative to nutcomponent for use with the embodiment of FIGS. 9 to 19;

FIG. 24 is a plan view of a further alternative nut component for usewith the embodiment of FIGS. 9 to 19;

FIG. 25 is an axial cross sectional view of the component of FIG. 24,taken along lines B-B of FIG. 24.

BEST MODE OF CARRYING OUT THE INVENTION

Referring to FIGS. 1 and 2, there is shown a self-locking fastener 10according to a first embodiment of the invention. The fastener 10 iscircular in plan view, but this is not essential. The fastener 10 isprovided with a blind, central bore 12. The bore 12 extends from theinner end 14 of the fastener toward the outer end 16. The bore 12 has aninner portion 18 and an outer portion 20. The diameter of portion 20 islarger than the diameter of portion 18. The inner end 14 is generallyplanar and perpendicular to the axis of the bore 12 but has a smallannular ring 22 extending around part of the outer portion 20 of thebore. The outer bore 20 has a length greater than that of the ring andso extends into the general body of the fastener. This is not importantand the length of the outer bore may the same as that of the ring 22 orit may be less. As will be explained later, one or both of the outerbore 20 and the annular ring 22 may be omitted. Where the outer bore isomitted, the bore 12 will preferably have a constant diameter along itslength.

The outer end 16 of the fastener is a truncated cone, but this is notessential and, for example, a planar surface perpendicular to the axisof the bore 12 or a part spherical or elliptical surface may beprovided. Located in the outer end 16 are two diametrically oppositeblind bores 24. These are shown as having a tapered inner end 26, butthis is not essential and a planar end may be provided.

The fastener 10 is manufactured from a resilient material and morepreferably a polyamide (Nylon) and more preferably PA 6E Nylon. However,other suitable materials may be used. The inner portion 18 of the bore12 is sized so that it may be screwed onto a suitable bolt, with thebolt forming a female thread into the bore 12 when inserted into thefastener. Thus the diameter of the inner portion 18 of the bore 12 isslightly less than the outside diameter of the threaded portion of thebolt and slightly greater then the inner diameter of the threadedportion of the bolt. Thus as the bolt is screwed onto the fastener, thematerial of the fastener adjacent the bore may be formed into a threadwithout removal of fastener material. For a {fraction (5/16)} inch(7.9375 mm) bolt, an inner diameter of about 7.19 mm provides a suitablecompromise between ease of attachment and tightness. Obviously othersize bolts will require appropriately sized bores.

In use the fastener is located on the free end of a bolt with the end ofthe bolt inserted into the outer portion 20 of the bore. The outerportion 20 serves to aid in centring the fastener on the bolt. Thefastener is then rotated using a suitable tool inserted into the twobores 24 whilst being pushed toward the bolt. This causes the bolt tocommence forming a thread in the bore. Once the bolt has been inserted asmall amount it is merely necessary to rotate the fastener relative tothe bolt, with the formed thread drawing the fastener onto the bolt.

The length of the bore 12 is such that for most situations the fastenerand bolt will become tight with the annular ring 22 limiting tighteningbefore the free end of the bolt contacts the blind end 26 of the bore.Thus when the fastener and bolt combination is assembled the free end ofthe bolt is protected within the fastener from damage.

The annular ring 22 serves at least two purposes. If the fastener 10 isbeing used to retain a bearing or a device with a bearing, such as askateboard wheel, the annular ring will contact the inner race of thebearing and prevent the fastener contacting the outer race of thebearing. A sealing and/or lubrication pad (not shown) may also be placedon the inner end 14 of the fastener around the ring 22 to serve as aprotective device for a bearing, so as to prevent or limit ingress ofdirt and debris into the bearing. The pad may be a felt disc andoptionally may be impregnated with oil or the like to providelubrication to the bearing. The diameter of the pad may be the same,greater or smaller than the diameter of the fastener, depending ofintended use. The pad may be made from other suitable materials.

FIGS. 3 and 4 show a self-locking fastener 30 according to a secondembodiment of the invention, substantially the same as the embodiment ofFIGS. 1 and 2. Accordingly, the same numerals are used to indicate thesame features. The fastener 30 has a circumferential groove 32 extendinginto the sidewall 34. This groove is adjacent the inner end 14 and isprovided so that a protective disc may be mounted on the side of thefastener in addition or as an alternative to mounting on the inner end.

FIGS. 5 and 6 show a self-locking fastener 40 according to a thirdembodiment of the invention. Features common to the embodiment of FIGS.1 and 2 are indicated with the same numbers. The fastener 40 is circularin plan view and has a similar truncated cone outer end 16. However, theinner end is planar, without an annular ring extending out of thegeneral plane of the inner end. As with the other embodiments, a blindbore 12 is provided, open at the inner end 14. The inner portion 18 ofthe bore is sized so that a bolt will form a thread. In contrast to theother embodiments, the outer portion 42 of the bore 12 is not a slightlyoversize circular bore. Instead the outer portion is a hexagonal recesssized to snugly accept a conventional nut of the size that will screwonto the same size thread as the inner portion 18. The recess ispreferably an interference fit with a conventional nut so that aconventional nut may be pushed into the recess 42 and retained. Theresilient nature of the material of the fastener 40 aids in retention ofthe conventional nut.

In use the conventional nut (not shown) is inserted into the recess 42and then threaded onto the bolt. If the nut may be screwed onto the boltso that the bolt extends through the conventional nut, the bolt willcommence to form a thread in the inner portion 18 of the bore 12, soaiding retention of the fastener 40 on the bolt. As with the first twoembodiments, the end of the bolt is protected from damage by the outerend 16 of the fastener 40. It will be appreciated, since the fastener 40utilises the conventional nut, that it is mainly intended as aprotective cap to prevent damage to the (normally) exposed end of thebolt, rather than as a retro fit after the bolt has been damaged.

FIGS. 7 and 8 show a self-locking fastener 50 according to a fourthembodiment of the invention, substantially the same as the embodiment ofFIGS. 1 and 2. Accordingly, the same numerals are used to indicate thesame features.

The fastener 50 is substantially the same as the fastener 10 of FIGS. 1and 2 except that it also has an annular ring 52 extending radiallyoutward from the circumferential side surface 54. The ring 52 is locatedadjacent the inner end 14 of the fastener 50, with its inner face 56coplanar with the inner end 14. It is not essential that the inner face56 is coplanar with inner end 14 and the ring 52 may be located awayfrom the inner end. The ring 52 provides some protection to a bearing orthe like. It will be appreciated that other materials, including thosepreviously mentioned, may be used for the various components.

Referring to FIGS. 9 to 19 there is shown a fifth embodiment of theinvention comprising a compound fastener 60. The fastener 60 includes ametal threaded inner nut 62, a washer 64 and a plastics or polymer outershell 66.

The fastener 60 is preferably formed by a plastics injection mouldingprocess with the nut 62 and the washer 64 encased in the shell 66.

The nut 62 includes first and second portions, 68 and 70. A bore 72centred on axis 71 extends through both portions and is provided with athread 73. The first portion 68 has a cylindrical outer surface 74 and aplanner outer end 76. It is not critical that the surface 74 becylindrical, as will be explained later. As seen in FIGS. 9 and 11 aportion 75 of the nut extends out of the shell 66.

The second portion 70, which is preferably formed integrally with theportion 68, in cross-section is planner and has a hexagonal shapedperiphery 78 and extends radially more than the first portion 68. Thesecond portion 70 serves to prevent the nut 62 being pulled axially outof the shell 66 and to prevent the nut 62 rotating about the axis 71. Assuch it is desirable that parts extend radially more than thecylindrical surface 74 and, if the first portion 68 is circular, theperiphery 78 is non-circular. It will be appreciated that the peripheryneed not be hexagonal and may be a polygon of any number of sides, suchas a triangle, quadrilateral, pentagon its etc. or may have anon-circular curved profile such as an oval or an ellipse. The peripherydoes not need to be a regular shape and may be an irregular shape.

It will be appreciated that the distinction between the two portions 68and 70 is somewhat artificial and that it is merely necessary that thenut 62 as a whole has features to prevent it being pulled out of theshell 66 and rotating relative to the shell 66. Thus we can consider theouter surface of the nut as a whole as requiring a surface portion thatis non-circular and a surface portion remote from the outer end 76 thatextends radially more than a part of the surface nearer to the outer end76. Thus, as an example, rather than having a T-shaped cross sectionalshape, a nut 62 may be provided with a non-circular peripheral surfacethat diverges from the outer end 76 to the inner end 79.

Located internally and within the shell 66 and coaxially with the nut 62is a resilient washer 64. The washer has a central bore 80 and anon-circular periphery 82. The diameter of the bore 80 is less than themaximum diameter of the thread 73 of the nut 62. In the embodiment shownin FIGS. 9 to 19 the diameter of the bore 80 is also a less than theminimum diameter or of the thread 73. In this embodiment the thread 73is a {fraction (5/16)}th inch UNF thread. This provides a maximumdiameter of 7.95 mm at the troughs of the thread and a minimum diameterof 6.85 mm at the peaks of the thread, as indicated by numerals 81 and83. The diameter of the bore 80 in the embodiment is 6.7 mm, which isless than the minimum diameter 83 of the thread 73. The washer 64 ispreferably formed of a resilient plastics or polymer material, such as aNylon. A preferred Nylon is PA 6E, but other suitable materials may beused.

The periphery 82 of the washer is also hexagonal and is preferably thesame size, in end view, as the hexagonal retaining portion 78 of the nut62. The periphery 82 in this embodiment is non-circular to preventrotation of the washer 64 in the shell 66. As such, the periphery 82 mayhave other non-circular shapes, such as a polygon, an oval, an ellipseor any other regular or irregular non-circular shape.

In addition or as an alternative to a non-circular periphery 82, thewasher may be provided with other features to prevent rotation. Examplesmay include one or more ribs on the inner surface 86 and/or depressionsor apertures extending into or through the washer 60 from the innersurface 86. When manufactured, the material of the shell 66 willsurround any ribs and enter any depressions or apertures and so preventrotation of the washer 64 relative to the shell 66.

The bore 80 is also sized to prevent, during manufacture, the shellmaterial entering into the threaded bore 71 of the nut 62, as explainedlater.

An example of an alternative washer 130 is shown in FIG. 22. The washer130 is a thin metal washer with a bore 132 smaller than the outer threaddiameter of the male thread. Extending outwardly from the periphery ofthe bore 132 are a, series of slits 132. Preferably the slits extendradially and more preferably they are spaced equally about theperiphery. The slits thus define a series of segments 138. Preferablythe bore 132 has a diameter larger than the minimum thread diameter ofthe male thread. Thus the segments 138 extend into the thread area ofthe male thread. In use the threads of the male component will engagethe edges of the bore and, due to the pitch of the thread, willelastically twist each segment 138 so as to be aligned with the thread.This results in frictional resistance to rotation of the bolt similar tothat provided by the resilient Nylon washer.

FIG. 23 shows a threaded component 140 that provides both retaining andinterfering functions. The component 140 has a threaded bore 142. Thebore 142 extends through the component to an inner end 144. The innerend 144 has one or more indents 146 punched or otherwise formed into thesurface so as to swage the adjacent portion of the thread to a reduceddiameter. When a bolt is threaded into the threaded component 140 fromthe outer end 148, it will freely engage the thread until it reaches theinner end 144. At this point the reduced diameter of the thread willfictionally engage the bolt and resist rotation.

FIGS. 24 and 25 show a further alternative threaded component 150. Thecomponent 150 is similar to the threaded component of FIGS. 9 to 19 butit has a slot 152 that extends axially along the full length of thecomponent. The slot 152 is crimped so as to be partially closed prior tothe component 150 being encased in the shell of the fastener. Thisreduces the diameter of the internal thread. Thus, as the bolt isscrewed into the thread of the component, there will be interference andso additional resistance to rotation of the bolt relative to thecomponent.

The shell 66 has two major portions, 90 and 92. The first portion 90 hasa substantially cylindrical outer wall 90 and encases the nut 62 and awasher 64. The second portion 92 is substantially a truncated cone, withan angled sidewall 94, a central, circular, planar end wall 96 andcurved intermediate walls 97 & 99. The curved intermediate walls 97 and99 are for manufacturing ease and to provide a more rounded appearanceto the fastener. The walls 97 and 99 are not essential and the angledwall 98 may extend between the cylindrical wall 90 and the end wall 96.It will be appreciated that for manufacturing purposes all cornerscannot be perfect angles and will have a small radius. In the preferredembodiments the overall exterior shape of the fastener is designed toprevent excess drag or fiction if the fastener scrapes against theground or another object.

Located in sidewall 94 are two diametrically opposed recesses 98. Therecesses 98 are cylindrical bores that extend to the washer 64. Therecesses 98 are to receive corresponding pins of a tightening spanner orwrench (not shown) and so need not be circular. The number of recessesmay be more than two, in which case the recesses will not be spaceddiametrically opposite to each other. Where three or more recesses areprovided they need not be spaced equally about the axis 71 of thefastener. The recesses 98 extend to the washer 64 for ease ofmanufacturing and it is not critical that they do so for the working ofthe fastener.

The recesses 98 are provided to enable the faster to be tightened,because the outer surfaces of the shell 66 are not conducive to beinggripped. It will be appreciated that a non-circular peripheral portionof the shell 66 will enable the fastener to be tightened without needinguse of the recesses 98. However, it is preferred that the shell 66 beshaped as in the drawings.

The shell 66 is also provided with a plain bore 100 that is coaxial tothe bores 71 and 80 extending through the nut 62 and a washer 64,respectively. The bore 100 is blind at an inner end 102. The diameter ofthe bore 100 in the embodiment preferably is the same as that of thebore 80 in the washer 64. This is mainly for ease of manufacturing andis not critical. The diameter 100 needs to be large enough to allow amale threaded axle or bolt to pass into the bore 100. As such a diametersmaller than the maximum thread diameter and optionally the minimumthread diameter it is acceptable. A clearance fit is also acceptable.Where the fit is an interference fit, that shell material is chosen sothat the male threaded component will form a thread in the shellmaterial, either by material being removed or by compressing ordistorting the material.

In use the fastener 60 is threaded onto a threaded axle or bolt and thethreaded axle engages thread 73 of the nut 62 and, as the fastener isrotated, the axle enters the bore until it reaches the washer 64. Thewasher is made of a resilient material. Thus, whilst the diameter of thebore in the washer 64 is smaller than the maximum thread diameter andoptionally the minimum thread diameter of the thread on the axle, theaxle forms a thread in the washer 64. This is achieved by displacing ordistorting the material of the washer 64. This restrains rotation of thefastener 60 relative to the axle, irrespective of whether the fasteneris tight or not, and so lessens the likelihood of the fastener becomingloose. Where the diameter of the bore 80 in the washer 64 is less thanthe minimum diameter of the thread on the axle, this means that therewill always be an interference fit between the washer and the axle, evenafter a thread has been formed in the washer 64.

The fastener is tightened onto the axle until the end 76 firmly engagesa surface being secured, such as the inner race of a bearing. Of course,one or more washers or spacers may be provided between a bearing and thefastener. As with the other embodiments, the diameter of the end 76 ischosen so that it will only contact the inner race. A lubricating and/orprotective washer (not shown) may be mounted on the inner end 76 of thefastener as described with reference to some of the other embodiments.

The embodiment of FIGS. 9 to 19 incorporates a separate washer 64 thatprovides a resilient member that resists rotation of the fastenerrelative to an engaged axle. It is not critical that a separate memberprovides this resistance. FIG. 20 shows a nut 120 that incorporatesfunction equivalent to the washer 64. The nut 120 includes at least oneplug of a resilient material inserted into a bore 110. The bore 110 maybe a blind bore that extends partially into the nut or it may be athrough bore that extends from the inner threaded surface 112 to theouter surface 114 of the nut 120. The plug 108 may have a length suchthat when fully inserted into the bore 110 it extends inwardly at leastbeyond the maximum diameter of the thread 73 and preferably extendsbeyond the minimum diameter of the thread 73. Where the bores 110 extendfully through the wall of the nut, it will be appreciated that prior tomanufacture the plugs 108 may be inserted into the bores from the outersurface of the nut until the outer end of the plug 108 is generallyflush with the outer surface of the nut. The nut 62 is then encased inthe shell 66 and so the plugs are prevented from radial outward movementby the shell material encasing the nut.

FIG. 21 shows a nut 130 that also incorporates a member functionallyequivalent to the washer 64. The nut 130 of FIG. 21 has one or moreslots 134 on the threaded surface 132. The slots 134 may extend parallelto the axis or may be angled to the axis. The slots 134 may extendthrough the wall of the nut or may only extend partially into the wallof the nut. The slots 134 may be straight but need not be. Located ineach slot 134 is a resilient member 136 that extends radially inwardsinto at least the zone of the thread 71 and preferably radially inwardlymore than the zone of the thread. Taking the embodiment of FIGS. 9 to 19as an example, the resilient members 124 will extend so that there innersurface 138 of the resilient member 124 is 6.7 mm from the axis 71compared to the inner diameter of the thread 71 being 6.85 mm from theaxis. The slot 120 may have a constant size through the wall of the nutor it may have a varying size. For example, in axial end view, thecross-sectional shape of the slot may be T-shaped. The resilient member124 may also be T-shaped or may be sized to merely fit into the widerportion of the slot. If the slot extends fully through the wall and isnot a fully filled by the resilient member 124, when the nut 120 isencased in the shell 66, the shell material will extend into the slot orslots and so aid in preventing rotation of the nut 120 relative to theshell.

Whilst all of the embodiments shown have a bore of constant crosssection, a tapering bore may be used instead with all the embodiments.The taper of the bore will be sufficient to improve the locking natureof the fastener whilst not preventing mounting of the fastener on thebolt.

All forms of the invention may be used with or without a washersandwiched between the inner end 14 of the fastener and the object beingsecured.

It will be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

Industrial Applicability

The invention has industrial applicability in providing protection ofexposed threads from damage.

1. A self locking fastener including: a blind bore sized to receive amale threaded component, the male component engaging or forming acomplementary thread on at least part of the inner surface of the blindbore, at least one first part of the bore being an interference fit withthe thread of the male threaded component, and an outer surface, theouter surface including at least two recesses located remote from theaxis of the bore, whereby the fastener may be rotated about the axis. 2.The fastener of claim 1 wherein a second part of the bore has a threadthat is a clearance fit with the thread of the male component.
 3. Thefastener of claim 2 wherein the at least one first part is locatedaxially coincident with at least part of the second part.
 4. Thefastener of claim 1 wherein at least part of the bore is defined by ashell.
 5. The fastener of claim 4 wherein the at least one first part isat least partially defined by the shell.
 6. The fastener of claim 1wherein the at least one first part is at least partially defined by aninterference component.
 7. The fastener of claim 6 wherein theinterfering component is a washer that has a bore through which thethreaded bolt passes.
 8. The fastener of claim 7 wherein the bore of thewasher is smaller than the outside diameter of the threaded bolt
 9. Thefastener of claim 7 wherein the diameter of the bore of the washersmaller than the inside diameter of the threaded bolt.
 10. The fastenerof claim 7 wherein the at least two recesses extend to the washer. 11.The fastener of claim 1 wherein the at least two recesses are parallelto the axis.
 12. The fastener of claim 2 including a separate threadedcomponent that defines at least some of the second part.
 13. Thefastener of claim 12 wherein the at least one first part is at leastpartially defined by an interfering component located axially coincidentwith a part of the threaded component and extending into the volumethrough which the male threaded component passes.
 14. The fastener ofclaim 13 wherein the interfering component includes one or more plugs ofa resilient material located in or on the thread of the threadedcomponent.
 15. The fastener of claim 12 wherein at least part of thethreaded component is located in a recess in the shell.
 16. The fastenerof claim 15 wherein the threaded component has an outer surface thatprevents the rotation off the threaded component relative to the shell.17. The fastener of claim 15 wherein the outer surface of the threadedcomponent has at least a portion that is non-circular when viewed alongthe axis of the bore.
 18. The fastener of claim 15 wherein the threadedcomponent has an outer surface that prevents the threaded componentbeing pulled out of the shell axially.
 19. The fastener of claim 15wherein the outer surface of the threaded component has a first portionand a second portion in which the second portion is located axiallyinwards in the shell compared to the first portion and extends radiallyfurther from the axis than the first portion.
 20. The fastener of claim12 wherein the threaded component has a cylindrical portion and ahexagonal portion located at one end of the cylindrical portion andwherein the hexagonal portion and at least substantially the entirecylindrical portion are encased in the shell.
 21. The fastener of claim20 wherein the hexagonal portion extends radially more than thecylindrical portion.
 22. The fastener of claim 1 wherein at least partof the outer surface having a profile selected from a group including acylinder, a polygon and an oval.
 23. The fastener of claim 22 wherein,when viewed along the axis, the outer surface is substantially circularor oval.
 24. The fastener of claim 1 wherein a free end part of thefirst portion extends out of the shell and, in use, bears against anobject being secured.
 25. The fastener of claim 1 wherein the malecomponent forms a female thread in the surface of the at least one firstpart when screwed into the bore.
 26. The fastener of claim 1 wherein theat least one first part is at least partially defined by a resilientmaterial.
 27. The fastener of claim 26 wherein the resilient material isa polyamide.
 28. The fastener of claim 1 wherein the diameter of thebore is tapered.